The present invention relates generally to ceramic coated abrasion resistant members and methods of manufacture. In particular, the invention is directed to such abrasion resistant members and methods of manufacture in which a plurality of thin plates of polycrystalline ceramic material are bonded to a thicker substrate member with an adhesive bonding material including a thermosetting organic plastic adhesive and a coupling agent which forms covalent chemical bonds with the organic plastic adhesive, the substrate base member and the ceramic plates. An organosilane has been used as such coupling agent with good success. The resulting ceramic coated abrasion resistant member is lightweight, extremely resistant to impact damage, has a long wear life, and has a bond of extremely great strength which will withstand high stress. The method of manufacture of such ceramic coated abrasion resistant member in accordance with the present is both simple and inexpensive.
The ceramic coated abrasion resistant member of the present invention is especially useful as an impeller blade for a fan used to convey abrasive particles, such as coal dust, through a conduit or as a blade for a pump impeller which may be used for pumping abrasive liquid. However, the invention is also suitable for use as an abrasive resistant dynamic bearing member which contacts a moving abrasive member, such as the stationary dewatering elements contacting the pulp conveyor wire of a Fourdrinier-type papermaking machine.
Previously, ceramic coated abrasion resistant members used as fan blades have been made by flame sprayed powder to produce a ceramic coating material on a metal substrate member. However, the resultant flame sprayed ceramic coatings are porous and of low density so that they are not sufficiently abrasion resistant and may even cause abrasion of any moving members in contact with them. Attempts have been made to bond a ceramic member to a metal substrate base member with epoxy resin or other thermosetting organic plastic adhesive. However, such bonds have failed because they are not of sufficient strength to resist the high stress such as created in a fan blade rotated at high speed. In order to solve this weak bonding problem, it has also been attempted to weld or solder plates of tungsten carbide ceramic material on the surface of a metal substrate base member. However, the resulting structure is extremely heavy and the bonds subject to metal fatigue so that under continued stress the solder joint eventually gives way causing the ceramic plates to come off the substrate. It is extremely dangerous when a ceramic plate breaks off a ceramic coated abrasion resistant member used as a high speed fan blade or impeller for a pump since the ceramic plate can easily cause extensive damage to the fan or pump and possible injury to workers. The above-mentioned problems have been overcome by the ceramic coated abrasion resistant member of the present invention.
Previously, it has been proposed in the Handbook of Adhesives by Irving Skeist, 1977 edition on pages 640-652 to provide high strength bonds with an organosilane coupling agent to bond fiberglass to resin for forming a fiberglass and resin laminated used in the manufacture of boat hulls and for other applications including grinding wheels. However, such a coupling agent has not previously been used to form a ceramic coated abrasion resistant member including a plurality of thin ceramic plates bonded to a thicker substrate member of metal or reinforced plastic material to form a continuous ceramic coating of higher hardness in the manner of the present invention.
In the papermaking industry it has been proposed to bond foil dewatering elements of ceramic which engage the lower surface of the Fourdrinier wire in the papermaking machine to a metal substrate with epoxy resin or other thermosetting plastic adhesive. In this regard, see U.S. Pat. No. 4,184,915 of Metcalfe, issued Jan. 22, 1980. However, the metal support member for the foil is thinner than the ceramic member to which it is bonded, and is not a substrate member on which a ceramic coating is applied. Thus, the ceramic member is not a coating and does not conform in shape to the surface of the metal member to which it is bonded. As a result, the ceramic abrasion resistant foil member is much heavier and more expensive to manufacture than the ceramic coated abrasion resistant member of the present invention. Furthermore, the bond of such foil did not include a coupling agent for greater strength, but was designed to enable breaking of the bond for removal of ceramic segments from the metal member without disturbing the other segments bonded thereto.